1. Field of the Disclosure
The present invention relates to a ring main unit circuit breaker equipped with a contact force controller, and particularly, to a ring main unit circuit breaker equipped with a contact force controller, capable of controlling a contact force between contacts of a vacuum interrupter, by controlling an interval between the contacts through a simple manual operation from outside, without having a disassembly operation.
2. Background of the Disclosure
Generally, a ring main unit (RMU) is a device configured to monitor, control and protect an electric system used when distributing power received from an electric power substation to consumers. The ring main unit is configured as an assembly which includes a circuit breaker, a switchgear, a ground switch, conducting lines, etc. in an enclosure insulated by SF6.
The circuit breaker of the ring main unit is generally provided with a vacuum interrupter. The vacuum interrupter is provided with a movable electrode and a fixed electrode which form a fixed contact and a movable contact contactable to or separable from each other. As a closing operation and an opening operation of the circuit breaker are repeatedly performed in an installation step and a usage step, the fixed contact and movable contact are pressed to thus be contracted. As the fixed contact and the movable contact are contracted, an interval between the contacts is increased. In this case, a contact force applied to the contacts may be decreased, and a contact failure may occur to cause an accident. Accordingly, the increased interval between the contacts should be restored to a normal state. In the conventional art, has been used a method for compensating a contact force by disassembling a circuit breaker, by upward-moving a fixed electrode of a vacuum interrupter using a spacer, and then by re-assembling the circuit breaker. However, such method requires complicated operations, i.e., an operation to disassemble the circuit breaker, an operation to control an interval between the contacts, and an operation to reassemble the circuit breaker. Details thereof will be explained below.
As a prior art of the ring main unit circuit breaker, Korean Registration Patent No. 10-1119734 (“MAIN CIRCUIT BREAKER FOR RING MAIN UNIT”) may be referred.
FIG. 1 is a perspective view of a ring main unit circuit breaker in accordance with the conventional art. FIG. 1 illustrates an entire appearance of a ring main unit circuit breaker where a vacuum interrupter 107 has been installed in a vertical direction, and an energy transmission structure. The circuit breaker includes a supporting member 103 fixedly-installed between a pair of supporting side walls 109; a rotational shaft 101 insertion-installed at the supporting member 103; a cam 102 configured to convert a rotation force of the rotational shaft 101 into a vertical force; a power transmission pin 104 which performs up-down movement by the cam 102; a movable rod 106 coupled to the power transmission pin 104; a contact spring 105 configured to provide a contact force to the movable rod 106; and a vacuum interrupter 107 having one end connected to the movable rod 106.
FIG. 2 illustrates a cam assembly configured to convert a rotation force of the rotational shaft 101 into a vertical force. The cam assembly includes a supporting member 103 configured to support the rotational shaft 101 in upper and lower directions, right and left directions, and back and forth directions; a bush 111 inserted into a body of the supporting member 103, and configured to transmit a driving force to the cam 102; and a cam 102 coupled to the bush 111 by welding.
FIG. 3 illustrates a circuit breaker re-assembled by further including a spacer 112 for compensation of a contact force which has been lost due to a pressed state of the fixed contact and the movable contact.
An operation of the conventional circuit breaker will be explained in more detail with reference to the attached drawings.
A rotation force of the rotational shaft 101, which is generated by a driving force received from a driving unit (not shown), is converted into a vertical force by the cam 102 having an inclined slot welded to the bush 111, and by the power transmission pin 104 restricted to move only in a vertical direction. Accordingly, the movable rod 106 coupled to the power transmission pin 104, and the movable electrode of the vacuum interrupter 107 which has been coupled to the movable rod 106 also move in a vertical direction. In a closing operation of the circuit breaker, the movable electrode of the vacuum interrupter 107 moves downward by receiving a vertical force. As a result, a movable contact of the movable electrode moves downward, thereby contacting a fixed contact of the fixed electrode. As the movable electrode continuously receives the vertical force, the contact spring 105 which provides a contact force is compressed. At the same time, the closing operation is completed in a state where a contact force applied to the fixed contact and the movable contact is maintained. On the contrary, if a force to maintain a closed state is removed in an open state, the movable electrode of the vacuum interrupter 107 is separated from the fixed electrode. Then the movable electrode moves upward, and the opening operation is completed.
As the closing operation and the opening operation of the circuit breaker are repeatedly performed, the fixed contact and the movable contact, formed of copper and disposed in the vacuum interrupter 107, are pressed by a mechanical impact applied thereto, and is gradually contracted. As the fixed contact and the movable contact are contracted, a contact force, applied to the fixed contact and the movable contact by the contact spring 105, is reduced to a value lower than an initial set value. For compensation of the contracted state of the fixed contact and the movable contact, the fixed electrode of the vacuum interrupter is displaced to a position higher than an initial assembly position, using the spacer 112. As the initial interval between the fixed contact and the movable contact is maintained, a contact force can be compensated.
In summary, the circuit breaker is designed so that a driving distance of the movable contact can be the sum of an interval between the fixed contact and the movable contact in an open circuit and a distance of the movable contact pressed by the contact spring. However, the contacts inside the vacuum interrupter 107 pressed by repeated opening and closing operations of the circuit breaker, to thus be contracted. As a result, an interval between the fixed contact and the movable contact is increased and thus a contact force of the contact spring 105 is decreased. In order to compensate for the decreased contact force due to the increased interval between the fixed contact and the movable contact, the circuit breaker sealed by insulating gas is disassembled in the conventional art. Also, the position of the fixed electrode of the vacuum interrupter 107 is upward moved using the spacer 112, thereby compensating the contracted length of the fixed contact and the movable contact. However, such disassembling operation of the circuit breaker, an operation to control the interval between the fixed contact and the movable contact and an operation to re-assemble the circuit beaker are complicated, and require a lot of time. Further, the circuit breaker may have a mal-operation due to the re-assembly of the circuit breaker.